1. Field of the Invention
The present invention falls within the technical field that relates to an ink composition for inkjet recording, an ink cartridge and a recording apparatus which are suitable for inkjet recording.
2. Description of the Prior Art
Conventionally, ink containing a colorant (dye or pigment), a humectant and water has been well known as ink used for inkjet recording. However, in the case of forming an image with the ink on a recording medium, the water-resistivity of the image is a matter of concern, i.e., there is a problem such that the colorant exudes into water when the image is exposed to water. Especially when an image is recorded on plain paper, the water-resistivity of the image is very poor. (The “plain paper” herein refers to paper which is one of various types of commercially-available paper, which is especially used for an electrophotographic copying machine, and which is produced without an intention to have an optimum structure, composition, properties, or the like, for inkjet recording.)
In Japanese Unexamined Patent Publication No. 10-212439, Japanese Unexamined Patent Publication No. 11-293167, Japanese Unexamined Patent Publication No. 11-315231, and Japanese Unexamined Patent Publication No. 2000-178494, adding a hydrolyzable silane compound (organic silicon compound) to ink in order to improve the water-resistivity of an image formed with the ink on a recording medium has been proposed. When a drop of such ink containing a silane compound is adhered on a recording medium, and a water content (solvent) of the ink drop evaporates or permeates into the recording medium, the silane compound remaining on the recording medium is condensation-polymerized, and this condensation-polymerized silane compound encloses a colorant. As a result, even when the image formed on the recording medium is exposed to water, the colorant is prevented from exuding into the water.
However, it was found that if such water-resistant ink containing the hydrolyzable silane compound is left in a high temperature environment (e.g., 40° C. or higher) for a long time, an aggregate which is hardly soluble or insoluble in water is generated. It is estimated that this problem is caused by the following reason. In the ink, the strength of an interaction between the colorant and the silane compound gradually increases so that the colorant encloses the silane compound to form an aggregate. The generation of the aggregate causes an ejection failure when the ink is ejected from a nozzle of an inkjet head.